In the past decade many developments have been made in the high speed finishing of wire rod production. Among these are the introduction of the no twist rod block and the development of "laying reel" coil forming heads. The combination of both of these techniques have increased the finishing speeds of rod rolling from 50 M/s to Over 100 M/s. Relatively little development has been made on the rolling of straight bars. This is because there is not much problem with the rolling of larger bars, for example, up to 12 mm diameter. However, for diameters of 10 mm down to 8 mm, the rolling mill has to operate at lower speeds and hence at reduced capacity. In my earlier patent 5,027,632, there is disclosed a method and apparatus for rolling a bar and feeding the rolled bar to a splitter without twisting the bar (the so-called NTA system). The NTA system substantially increases the finishing speeds, but other problems still exist when a smaller diameter bar is fed to the cooling bed at a high speed.
Essentially, a run-in table receives the bars at high speed and the run-in table should theoretically be as smooth as possible to avoid contact of the front end of the bar with any protruding parts causing a cobble. Unfortunately, there are other functions that the run-in table has to perform and a smooth uninterrupted surface is not possible. Systems requiring limitation on the maximum length of the installation of a closed channel system pose additional maintenance difficulties.
A steel bar entering the run-in table of the cooling bed at a high speed would require a very long distance for the bar to slow down before it can be discharged onto the cooling bed for cooling purposes. Such long distances require much space and unnecessary expense in the construction of a building to accommodate the extra space. The braking distance is proportional to the square of the finishing speed in the case of natural braking. In order to reduce this braking distance, external brakes are employed.
Two known methods for braking the bars are as follows:
1) Braking by pinch rollers, (FIG. 1) whereby the steel bar 1 is passed through a pair of pinch rollers 2. The pinch rollers 2 serve two purposes, first, the pinch rollers accelerate the bar that has been cut to cooling bed length by flying shears 3 to separate it from the incoming bar and second the pinch rollers 2 are driven in reverse direction to brake the steel bar 1 to a manageable speed before discharge onto rakes of the cooling bed. This method has the disadvantage that it may cause damage to the surface of the steel bar. With this system, it is not required to install additional rollers along the run-in table of the cooling bed.
2) Braking by magnetic pads (FIG. 2) wherein magnetic pads 4 are installed under the lifting aprons of the run-in table. Upon energizing of the magnetic pads 4, the friction between the steel bar and the lifting table surface is increased thereby slowing the bar down. With this arrangement, additional rollers 5 are required along the lifting apron in order to accelerate the cut portion of the steel bar to separate the incoming bars after the flying shears 3. The top surfaces of rollers 5 must protrude above the level of the lifting apron in order to have contact with the steel bars. This can cause a "bouncing effect" on the front end of the steel bars, when the front end of the bar hits the top surface of the rollers. This may be a potential hazard for producing cobbles in the cooling bed.